Many methods of welding are known in the art, each with its own advantages and disadvantages. Common welding processes include gas welding, oxyacetylene brazing and soldering, shielded metal arc welding (SMAW) or "STICK" welding, metal inert gas (MIG) or "wire feed" welding, and gas tungsten arc welding (GTAW) or "TIG" welding. Known welding power supplies provide the necessary welding power, gas supply, and other welding inputs needed to perform one or more of the various welding processes. While the present invention will be described with reference to a welding device having TIG and STICK capabilities, one skilled in the art will appreciate that the present invention may have applications in many other welding power supplies.
Since most welding power supplies are designed to be operated by a human operator, various types of remote control devices adapted for human interface have been introduced to facilitate operator control of the welding processes. The art of welding often requires the operator to select and adjust numerous operating parameters of the welding device, including, the welding process itself, the flow of shielding gas to the weld site and, in some welding processes, various characteristics of the welding arc (e.g., current or amperage, pulse frequency, initial slope, final slope, etc.). These operating parameters can be adjusted using parameter selectors on the control panel of the welding device. Some of the adjustments, however, are more conveniently made by employing a remote control device to control, for example, the beginning and end of a welding cycle and/or the current of the welding arc (i.e., the welding current). For example, in a TIG welding process, a trigger on a fingertip control remote device is pressed to begin a welding cycle, varied through a range of positions to control the magnitude of the welding current, then released to end the welding cycle.
Numerous types of remote devices exist in the art, and others have yet to be developed. The present invention will find applications with all types of remote devices. A "trigger only" remote device is either a foot or hand control device including a simple on/off switch. A "hand control" remote device includes a box having a potentiometer including an operator input device (e.g., a dial) to control an operating parameter, and a switch independently coupled to the box to provide an on/off signal. A "fingertip control" or "foot control" remote device, as used herein, includes a "switchpot", i.e., a potentiometer and a switch tied together such that movement of an operator input device controls both the switch and the potentiometer. Both the hand control remote device and the fingertip/foot control remote devices are capable of controlling an operating parameter, such as, welding current, over a range of values.
While the addition of a remote control device to a welding device can add convenience and flexibility to the welding process, it can also add confusion to the operator over which control device is actually controlling the operating parameter. In one prior art welding device, an operating parameter selector, including a panel-mounted knob coupled to a potentiometer, is coupled through a high-impedance series resistor to a control circuit. By adjusting the knob, the operator varies an operating parameter control signal provided to the control circuit. When a remote device, having a potentiometer with a relatively low impedance, is coupled in parallel with the selector and high-impedance resistor, current travels preferably through the lower impedance potentiometer of the remote device, allowing the remote device to control the operating parameter. However, if the operator leaves the welding device and later returns, the operator may not notice that the remote device is still coupled to the welding device and may attempt to adjust the operating parameter using the panel-mounted knob.
Another limitation of the prior art occurs when the operator wishes to switch from a TIG welding process using an attached fingertip or foot control remote device to a STICK welding process. STICK welding typically cannot be done with a fingertip or foot control remote device. Accordingly, the operator must always remember to remove the remote device from the welding device when switching from a TIG welding process to a STICK welding process or actuate another switch on the control panel. With increased productivity demands of professional welders, the welder can forget to remove the remote device when switching from one process to another which, again, results in operator confusion and bad welds.
In another known system, a control circuit is provided for sensing when a remote potentiometer is electrically connected therewith and disconnected therefrom. The control circuit includes a switching arrangement for receiving a first control signal from a local current setting device and a second control signal from a remote current setting device. The control circuit selectively connects one of the first and second control signals with a power supply and disconnects the other of the first and second control signals with the power supply based on whether the remote current setting device is coupled to the control circuit. This system, however, has several limitations. First, the system cannot detect the type of remote device coupled to the power supply; it can only determine whether or not any remote device is coupled to the power supply. Second, the system utilizes costly switching elements (e.g., relays) to electrically isolate portions of the control circuit to selectively connect and disconnect the control signals to the power supply. Also, the system requires a STICK/TIG switch to physically disconnect the remote control device during STICK welding.
Yet another limitation of the prior art is that known hand control remote devices do not clearly identify the magnitude of the operating parameter they are controlling. Thus, setting the dial of the hand control at the middle of its range of motion does not necessarily indicate 50% of the maximum value of the operating parameter. Therefore, the operator receives no accurate indication from the hand control and power source of how much welding current is being provided to the welding arc.
What is needed is an improved welding device that overcomes these and other limitations of prior welding power supplies. The improved welding device would have the capability to determine not just whether a remote device exists, but what type of remote device is coupled to the welding device. The improved welding device also would be substantially free of relays and other expensive switching circuitry. The improved welding device would further include sufficient intelligence to select which of local and remote control signals controls the welding current based on a selected welding process.